Alkylation/1,2-aryl migration of α-aryl allylic alcohols with α-carbonyl alkyl bromides using visible-light photoredox catalysis

Abstract

A novel visible-light-induced alkene difunctionalization strategy is described for the synthesis of 1,5-dicarbonyl compounds from two reaction partners, α-aryl allylic alcohols and α-carbonyl alkyl bromides. This method is successful by sequential alkylation of an alkene C–C double bond and intramolecular 1,2-aryl migration, and shows a broad substrate scope, excellent functional group tolerance and good selectivity.

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Introduction

Alkenes represent an important class of chemical feedstock with broad utility in organic synthesis for the construction of more complex molecular entities. Thus, methods for the efficient functionalization of alkenes at the C–C double bond positions are of intense interest.^1,2 Particularly attractive are the alkene difunctionalization transformations wherein two functional groups are introduced across alkenes in a catalytic and selectivity-controlled manner.^2–7 Despite remarkable progress in the alkene difunctionalization field, the dicarbofunctionalization of alkenes involving the simultaneous incorporation of an arene group and an alkyl group has been more limited^3–7 and mostly restricted to the requirement of a stoichiometric amount of oxidants (often hypervalent iodine reagents or peroxides) and the synthesis of oxindoles and related heterocycles.^3–5,7 Liu's group had first reported the alkylarylation of activated alkenes with aryl C(sp²)–H bonds and alkyl C(sp³)–H bonds adjacent to a CN group in the presence of Pd(II) catalysts and hypervalent iodine reagents to assemble CN-containing oxindoles.³ Later, our group illustrated an oxidative alkylarylation of activated alkenes with aryl C(sp²)–H bonds and alkyl C(sp³)–H bonds adjacent to a heteroatom (O, S or N atom) for the synthesis of functionalized 3-(2-oxoethyl)indolin-2-ones using the Fe catalyst/peroxide system.⁴ The group of Liu,^5a the group of Cheng^5b and our group^5c have independently described that similar transformations could be achieved using hypervalent iodine reagents or peroxides as the alkyl resources. The group of Xu/Ji developed a metal-free peroxide-mediated alkylarylation of alkenes (α,α-diaryl allylic alcohols) with alkyl C(sp³)–H bonds adjacent to an oxygen atom through intramolecular 1,2-aryl migration.⁶ A Pd-catalyzed oxidative Heck-type insertion strategy for the alkylarylation of activated alkenes with aryl C(sp²)–H bonds and α-C(sp³)-Br bonds in α-carbonyl alkyl bromides, which has very recently been reported by our group, appears to be a good alternative; however, such a process is limited to an activated system, thus only enabling intramolecular aryl C(sp²)–H functionalization to access oxindoles and related heterocycles.⁷ Thus, further discovery of a new mild strategy for general alkylarylation of alkenes leading to diverse complex molecules is highly desirable.

Recently, visible-light photoredox catalysis has proven to be a powerful and environmentally benign methodology for the construction of various C–C bonds in synthesis.^8–11 In the field, alkene functionalization initiated by the in situ generation of alkyl radicals from alkyl halides through atom transfer radical addition (alkylation–halogenation),⁹ hydroalkylation (Scheme 1a)¹⁰ and alkenylation (Scheme 1b)¹¹ have been well explored. Herein, we report a novel visible-light photoredox catalysis strategy for the alkylarylation of α-aryl allylic alcohols with α-carbonyl alkyl bromides through alkylation/1,2-aryl migration (Scheme 1c).¹² This visible-light photoredox catalysis is applicable to a wide range of α-carbonyl alkyl bromides, including primary-, secondary- and tertiary-α-bromoalkyl esters, ketones and amides, and even the more challenging 2-bromo-2,2-difluoroacetate.

Scheme 1 Functionalization of alkenes with alkyl halides using visible-light photocatalysis.

Results and discussion

We started optimization studies by investigating the reaction between 1,1-diphenylprop-2-en-1-ol (1a) and 2-bromoacetophenone (2a), a primary alkyl bromide, using the visible-light photoredox catalysis strategy (Table 1). The results demonstrated that among the three photocatalysts [Ir(ppy)₃] was more efficient than [Ru(bpy)₃Cl₂] and eosin (entries 1–3). In the presence of 2 mol% [Ir(ppy)₃], 1.2 equiv. Ag₂CO₃ and 36 W compact fluorescent light, the desired alkylation/1,2-phenyl migration product 3aa was formed from substrate 1a and alkyl bromide 2a in 90% yield (entry 1). Notably, a photocatalyst was necessary for successful alkylation/1,2-aryl migration, as its absence resulted in no detectable product 3aa (entry 4). The amount of [Ir(ppy)₃] was found to affect the reaction, as 2 mol% [Ir(ppy)₃] was preferred (entry 1 versus entries 4 and 5). However, the yield of 3aa decreased to 55% using 5 W blue LED light instead of 36 W compact fluorescent light (entry 1 versus entry 6). In addition, the reaction did not take place without additional visible light (entry 7). It should be noted that the reaction could occur without bases, albeit with a lower yield (23% yield, entry 8). Extensive screening of the effect of bases revealed that adding a base, such as Ag₂CO₃, Ag₂O, AgOAc, Na₂CO₃ and NaOH, improved the reaction, and using 1.2 equiv. Ag₂CO₃ was the best choice (entry 1 versus entries 8–14). After varying reaction temperatures and solvents, we found that this reaction in MeCN at 50 °C gave the best results (entry 1 versus entries 15–18). We were delighted to find that a reaction on a 1 gram scale of substrate 1a was successfully performed in good yield (entry 19).

Table 1 Screening of the reaction conditions^a

Entry	[M] (mol%)	Base (equiv.)	Solvent	T (°C)	Yield (%)
a Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), [M], base and solvent (2 mL) with 36 W compact fluorescent light under an argon atmosphere for 16 h. b 5 W blue LED light instead of 36 W compact fluorescent light. c Without additional light. d 1a (1 g, 4.76 mmol) for 72 h.
1	[Ir(ppy)3] (2)	Ag2CO3 (1.2)	MeCN	50	90
2	[Ru(bpy)3Cl2] (2)	Ag2CO3 (1.2)	MeCN	50	8
3	Eosin Y (2)	Ag2CO3 (1.2)	MeCN	50	5
4	—	Ag2CO3 (1.2)	MeCN	50	0
5	[Ir(ppy)3] (5)	Ag2CO3 (1.2)	MeCN	50	91
6^b	[Ir(ppy)3] (2)	Ag2CO3 (1.2)	MeCN	50	55
7^c	[Ir(ppy)3] (2)	Ag2CO3 (1.2)	MeCN	50	0
8	[Ir(ppy)3] (2)	—	MeCN	50	23
9	[Ir(ppy)3] (2)	Ag2CO3 (2)	MeCN	50	90
10	[Ir(ppy)3] (2)	Ag2CO3 (1)	MeCN	50	85
11	[Ir(ppy)3] (2)	Ag2O (1.2)	MeCN	50	52
12	[Ir(ppy)3] (2)	AgOAc (1.2)	MeCN	50	62
13	[Ir(ppy)3] (2)	Na2CO3 (1.2)	MeCN	50	75
14	[Ir(ppy)3] (2)	NaOH (1.2)	MeCN	50	35
15	[Ir(ppy)3] (2)	Ag2CO3 (1.2)	MeCN	rt	60
16	[Ir(ppy)3] (2)	Ag2CO3 (1.2)	MeCN	80	45
17	[Ir(ppy)3] (2)	Ag2CO3 (1.2)	toluene	50	50
18	[Ir(ppy)3] (2)	Ag2CO3 (1.2)	DMF	50	13
19^d	[Ir(ppy)3] (2)	Ag2CO3 (1.2)	MeCN	50	92

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Having established the optimal reaction conditions, we turned our attention to investigate the scope of this alkylation/1,2-aryl migration protocol with respect to α-aryl allylic alcohols 1 and α-carbonyl alkyl bromides 2 (Tables 2 and 3). First, we explore this new transformation by using different α-carbonyl alkyl bromides 2b–m, including primary-, secondary- and tertiary-α-bromoalkyl ketones, esters and amides, and 2-bromo-2,2-difluoroacetate, to react with 1,1-diphenylprop-2-en-1-ol (1a), [Ir(ppy)₃], Ag₂CO₃ and 36 W compact fluorescent light (Table 2). The optimal conditions proved to be compatible with both primary-α-bromoalkyl ketones 2b–e and ester 2f, giving the corresponding alkylation/1,2-aryl migration products 3ab–af in moderate to excellent yields. In addition, in ketones 2b–e the electronic properties of the substituted aryl groups affected the reaction, and their reactive order is as follows: electron-rich > electron-deficient. A number of secondary-α-bromoalkyl ketones 2g, esters 2h and amides 2i–j also worked well and led to the desired products 3ag–aj in moderate to good yields, although ketone 2g had the least reactivity. The alkylation/1,2-aryl migration of 1,1-diphenylprop-2-en-1-ol (1a) with tertiary-α-bromoalkyl esters 2k and 2l successfully afforded 3ak and 3al in high yields with excellent levels of regioselective control. Interestingly, 2-bromo-2,2-difluoroacetate (2m) also had high reactivity and delivered a two fluoro atom-containing product 3am in 88% yield.

Table 2 Variation of the α-carbonyl alkyl bromides (2)^a

a Reaction conditions: 1a (0.2 mmol), 2 (0.4 mmol), [Ir(ppy)₃] (2 mol%), Ag₂CO₃ (1.2 equiv.) and MeCN (2 mL) with 36 W compact fluorescent light at 50 °C under an argon atmosphere.

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Table 3 Variation of the α-aryl allylic alcohols (1)^a

a Reaction conditions: 1 (0.2 mmol), 2 (0.4 mmol), [Ir(ppy)₃] (2 mol%), Ag₂CO₃ (1.2 equiv.) and MeCN (2 mL) with 36 W compact fluorescent light at 50 °C under an argon atmosphere for 18 h. The ratio of product 3/its isomer is given in parenthesis determined by GC-MS or ¹H NMR analysis of the crude product. b For 24 h.

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We next set out to apply the optimal conditions to the alkylation/1,2-aryl migration of various α-aryl allylic alcohols 1 with 2-bromoacetophenone (2a), methyl 2-bromopropanoate (2h), diethyl 2-bromo-2-methylmalonate (2l) or 2-bromo-2,2-difluoroacetate (2m) (Table 3). In the presence of 2-bromoacetophenone (2a), [Ir(ppy)₃], Ag₂CO₃ and 36 W compact fluorescent light, alcohols 1b–d, which contain two same substituted aryl groups, including two 4-MePh, two 4-ClPh and 4-BrPh groups, on the α-position chemospecifically furnished 3ba–3da in moderate to good yields. Alcohols 1e–s, which contain two different substituted aryl groups, were also viable substrates for the alkylation/1,2-aryl migration reaction, and selectivity of their products 3ea–3sa toward the migrating aryl group relied on the electronic and steric hindrance properties of the α-substituted aryl groups. For alcohols 1e–f, the Ph group was the major migration group in alcohols 1e and 1f (products 3ea and 3fa ^12c,j) (product 3ea, two regioisomers are not separated by silica gel column chromatography). Alcohols 1g–h, containing other two substituents – a α-Ph group and a α-4-substituted Ph group – provided the α-4-substituted Ph migrating products 3ga–3ha^12c,j as the major isomers in high yield. While the α-Ph group and the α-3-MePh group in alcohol 1i had the same migrating chance (product 3ia), in alcohol 1j the migration of the α-3-CF₃Ph group had precedence over the α-Ph group (product 3ja^6a,12f–h). For the α-Ph group vs. α-3,4-disubstituted Ph groups, the former was a major migration group (product 3ka^6a,12f–h) and the latter was a major migration group (product 3la^12c,j). Notably, the sterically hindered α-2-substituted Ph groups were not good migrating groups: the migration of the α-Ph group or the α-4-ClPh group was found to be preferred during the reaction of alcohols 1m–q (products 3ma–qa).^12c,j Using 1-(naphthalen-2-yl)-1-phenylprop-2-en-1-ol (1r) to react with 2-bromoacetophenone (2a) delivered the α-naphthalen group migrating product 3ra ^12p as the major product in 58% yield. The α-Ph- and α-thiophen-2-yl-substituted alcohol 1s also worked well and mainly provided the thiophen-2-yl-migrating product 3sa in 85% yield. Interestingly, the reaction was applicable to 2-phenylbut-3-en-2-ol (1t), exclusively giving the Ph-migrating product 3ta in 75% yield.

The rule of α-substituted aryl group migration applies to alcohols 1 with other α-carbonyl alkyl bromides. For example, the α-Ph- and α-2-Cl-substituted alcohol 1n reacted with methyl 2-bromopropanoate (2h), diethyl 2-bromo-2-methylmalonate (2l) or 2-bromo-2,2-difluoroacetate (2m) and mainly delivered the Ph-migrating products 3nh, 3nl and 3nm in 75–85% yield. Notably, the reaction with diethyl 2-bromo-2-methylmalonate (2l) was finished quickly (18 h) in contrast with the results of Yang and Xia's group (143 h).^12p

As shown in Scheme 2, a control experiment using a mixture of two different α-aryl allylic alcohols 1a and 1c reacted with 2-bromoacetophenone (2a) under the optimal conditions was conducted to gain some mechanistic insight into the alkylation/1,2-aryl migration protocol. The results demonstrated that no cross aryl-migrating product 3ga was observed, suggesting that the 1,2-aryl migration proceeds via an intramolecular process. Notably, three radical inhibitors (2.5 equiv.), TEMPO, hydroquinone and BHT, were added to the reaction of alcohol 1a with 2-bromoacetophenone (2a) and resulted in no detectable product 3aa, implying that this current reaction includes a radical process.

Scheme 2 Control experiment.

An off/on light profile over time was also illustrated to understand the mechanism of this photoredox alkylation/1,2-aryl migration insertion (Fig. S1 in the ESI†). The results show that the additional visible light is necessary for the current reaction: the reaction successfully proceeds upon irradiation with light, but the absence of the additional visible light results in no further conversion. These results suggest that the current reaction follows a photoredox mechanism.

Consequently, a possible mechanism outlined in Scheme 3 was proposed on the basis of the above results as well as previous studies.^8–12 Initially, the active Ir³⁺ species is irradiated to the excited state Ir³⁺˙ species by visible light.^8–11 Single-electron transfer (SET) between the Ir³⁺˙ species and 2-bromoacetophenone (2a) readily takes place to form alkyl radical A and the Ir⁴⁺ species. Subsequently, the addition of alkyl radical A to the C–C double bond of 1,1-diphenylprop-2-en-1-ol (1a) leads to a new alkyl radical intermediate B. Within intermediate B, 1,2-migration of the aryl group occurs via spiro^2,5 octadienyl radical C, giving intermediate D.¹² Finally, intermediate D is oxidized by the Ir⁴⁺ species to afford the cationic intermediate E and regenerate the active Ir³⁺ species, followed by deprotonation of the cationic intermediate E giving the desired product 3aa.

Scheme 3 Possible mechanism.

Conclusions

In summary, we have illustrated a highly efficient and practical alkylation/1,2-aryl migration of α-aryl allylic alcohols with α-carbonyl alkyl bromides through visible-light photoredox catalysis. This new method successfully works with primary, secondary and tertiary α-bromoalkyl carbonyl compounds or 2-bromo-2,2-difluoroacetate to produce 1,5-dicarbonyl compounds with different substitution patterns in good yields, which represents the first visible-light-induced alkylarylation of alkenes using the 1,2-aryl migration strategy with a broad substrate scope, excellent selectivity and mild reaction conditions.

Experimental section

General considerations

The ¹H and ¹³C NMR spectra were recorded in CDCl₃ solvent on a NMR spectrometer using TMS as the internal standard. LRMS was performed on a GC-MS instrument and HRMS was recorded on an electrospray ionization (ESI) apparatus using time-of-flight (TOF) mass spectrometry. Melting points are uncorrected.

Typical experimental procedure for alkylation/1,2-aryl migration of α-aryl allylic alcohols with α-carbonyl alkyl bromides using visible-light photoredox catalysis

To a Schlenk tube were added α-aryl allylic alcohols 1 (0.2 mmol), α-carbonyl alkyl bromides 2 (0.4 mmol), [Ir(ppy)₃] (2 mol%), Ag₂CO₃ (1.2 equiv.), and MeCN (2 mL). Then the tube was charged with argon, and was stirred at 50 °C (oil bath temperature) with 36 W compact fluorescent light under an argon atmosphere for the indicated time until complete consumption of the starting material as monitored by TLC and/or GC-MS analysis. After the reaction was finished, the reaction mixture was cooled to room temperature, diluted in diethyl ether, and washed with brine. The aqueous phase was re-extracted with diethyl ether. The combined organic extracts were dried over Na₂SO₄ and concentrated in vacuum, and the resulting residue was purified by silica gel column chromatography (hexane/ethyl acetate) to afford the desired products 3.

1,2,5-Triphenylpentane-1,5-dione (3aa). 59.0 mg, 90%; White solid; mp 81.1–82.3 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.98 (d, J = 7.2 Hz, 2H), 7.90 (d, J = 7.6 Hz, 2H), 7.52 (t, J = 7.2 Hz, 1H), 7.47 (m, 5H), 7. 29 (d, J = 7.2 Hz, 4H), 7.21 (d, J = 6.8 Hz, 1H), 4.78 (t, J = 6.8 Hz, 1H), 3.05–2.89 (m, 2H), 2.63–2.55 (m, 1H), 2.32–2.24 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.9, 199.6, 139.1, 136.7, 136.6, 133.0, 132.9, 129.0, 128.7, 128.5, 128.5, 128.3, 128.0, 127.2, 52.4, 35.9, 28.2; IR (KBr, cm⁻¹): 1686, 1674; LRMS (EI, 70 eV) m/z (%): 329 (M⁺ + 1, 18), 328 (M⁺, 11), 223 (10), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₂₁O₂ ([M + H]⁺) 329.1536, found 329.1523.

1,2-Diphenyl-5-(p-tolyl)pentane-1,5-dione (3ab). 56.1 mg, 82%; White solid; mp 87.8–88.6 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.97 (d, J = 7.2 Hz, 2H), 7.80 (d, J = 7.6 Hz, 2H), 7.46 (t, J = 7.2 Hz, 1H), 7.37 (t, J = 7.2 Hz, 2H), 7.29 (t, J = 8.0 Hz, 4H), 7.21 (d, J = 7.6 Hz, 3H), 4.77 (t, J = 7.2 Hz, 1H), 3.02–2.85 (m, 2H), 2.62–2.54 (m, 1H), 2.38 (s, 3H), 2.31–2.22 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.7, 199.6, 143.8, 139.1, 136.6, 134.3, 132.9, 129.2, 129.0, 128.7, 128.5, 128.3, 128.1, 127.2, 52.4, 35.8, 28.3, 21.6; IR (KBr, cm⁻¹): 1686, 1665; LRMS (EI, 70 eV) m/z (%): 343 (M⁺ + 1, 8), 342 (M⁺, 13), 238 (26), 105 (100); HRMS m/z (ESI) calcd for C₂₄H₂₃O₂ ([M + H]⁺) 343.1693, found 343.1699.

5-(4-Methoxyphenyl)-1,2-diphenylpentane-1,5-dione (3ac). 51.6 mg, 72%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.97 (d, J = 7.2 Hz, 2H), 7.89 (d, J = 7.6 Hz, 2H), 7.47 (t, J = 7.2 Hz, 1H), 7.37 (t, J = 7.2 Hz, 2H), 7.30 (s, 4H), 7.20 (s, 1H), 6.89 (d, J = 7.6 Hz, 2H), 4.77 (t, J = 6.8 Hz, 1H), 3.84 (s, 3H), 3.00–2.83 (m, 2H), 2.62–2.54 (m, 1H), 2.30–2.22 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.7, 198.5, 163.4, 139.2, 136.6, 132.9, 130.3, 129.9, 129.0, 128.7, 128.5, 128.3, 127.2, 113.6, 55.4, 52.5, 35.6, 28.5; IR (KBr, cm⁻¹): 1686, 1649; LRMS (EI, 70 eV) m/z (%): 359 (M⁺ + 1, 10), 358 (M⁺, 6), 207 (10), 150 (31), 105 (100); HRMS m/z (ESI) calcd for C₂₄H₂₃O₃ ([M + H]⁺) 359.1642, found 359.1655.

5-(4-Fluorophenyl)-1,2-diphenylpentane-1,5-dione (3ad). 38.7 mg, 56%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.98–7.91 (m, 4H), 7.47 (t, J = 7.6 Hz, 1H), 7.38 (t, J = 7.6 Hz, 2H), 7.30–7.27 (m, 4H), 7.24–7.18 (m, 1H), 7.09 (t, J = 8.6 Hz, 2H), 4.76 (t, J = 7.6 Hz, 1H), 3.02–2.85 (m, 2H), 2.62–2.53 (m, 1H), 2.31–2.23 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.5, 198.3, 167.2 (d, J = 253.1 Hz), 139.1, 136.6, 133.2, 133.0, 130.7, 129.0, 128.8, 128.5, 128.3, 127.3, 115.6, 52.4, 35.9, 28.3; ¹⁹F NMR (375 MHz, CDCl₃) δ: −105.3 (m); IR (KBr, cm⁻¹): 1686, 1660; LRMS (EI, 70 eV) m/z (%): 347 (M⁺ + 1, 16), 346 (M⁺, 14), 209 (8), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₂₀FO₂ ([M + H]⁺) 347.1442, found 347.1448.

4-(5-Oxo-4,5-diphenylpentanoyl)benzonitrile (3ae). 40.9 mg, 58%; White solid; mp 101.7–102.5 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.97 (t, J = 7.2 Hz, 4H), 7.74 (d, J = 7.6 Hz, 2H), 7.49 (t, J = 7.2 Hz, 1H), 7.39 (t, J = 7.6 Hz, 2H), 7.29 (s, 4H), 7.22 (s, 1H), 4.74 (t, J = 7.2 Hz, 1H), 3.07–2.90 (m, 2H), 2.62–2.55 (m, 1H), 2.33–2.26 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.3, 198.5, 139.6, 138.9, 136.4, 133.1, 132.5, 129.2, 128.8, 128.6, 128.4, 128.2, 127.4, 117.9, 116.3, 52.4, 36.4, 28.1; IR (KBr, cm⁻¹): 1686, 1653; LRMS (EI, 70 eV) m/z (%): 354 (M⁺ + 1, 20), 353 (M⁺, 11), 246 (16), 105 (100); HRMS m/z (ESI) calcd for C₂₄H₂₀NO₂ ([M + H]⁺) 354.1488, found 354.1489.

Ethyl 5-oxo-4,5-diphenylpentanoate (3af). 56.8 mg, 96%; Yellow oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.94 (d, J = 7.2 Hz, 2H), 7.45 (t, J = 7.6 Hz, 1H), 7.36 (t, J = 7.6 Hz, 2H), 7.29–7.25 (m, 4H), 7.23–7.17 (m, 1H), 4.68 (t, J = 7.2 Hz, 1H), 4.13–4.07 (m, 2H), 2.50–2.42 (m, 1H), 2.31–2.73 (m, 2H), 2.21–2.13 (m, 1H), 1.21 (t, J = 7.2 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.2, 173.2, 138.7, 136.5, 132.9, 129.0, 128.6, 128.4, 128.2, 127.2, 60.3, 52.3, 31.8, 28.7, 14.1; IR (KBr, cm⁻¹): 1708, 1686; LRMS (EI, 70 eV) m/z (%): 297 (M⁺ + 1, 19), 296 (M⁺, 13), 117 (21), 105 (100); HRMS m/z (ESI) calcd for C₁₉H₂₁O₃ ([M + H]⁺) 297.1497, found 297.1485.

4-Methyl-1,2-diphenylhexane-1,5-dione (3ag). d.r. = 3 : 2; 26.9 mg, 48%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.97–7.92 (m, 2.0H), 7.48 (t, J = 7.2 Hz, 1.0H), 7.38 (t, J = 7.2 Hz, 2.0H), 7.30–7.21 (m, 5.0H), 4.66–4.61 (m, 1.0H), 2.49–2.39 (m, 1.3H), 2.19 (t, J = 6.8 Hz, 1.0H), 2.13 (s, 1.8H), 2.03 (s, 1.2H), 1.90–1.82 (m, 0.7H), 1.16 (d, J = 5.6 Hz, 1.2H), 1.09 (d, J = 6.0 Hz, 1.8H); ¹³C NMR (100 MHz, CDCl₃) δ: 212.4, 212.3, 199.5, 199.4, 139.2, 138.9, 136.6, 136.5, 133.0 (2C), 129.1, 129.0, 128.7, 128.7, 128.6, 128.5, 128.3, 128.1, 127.3, 127.2, 51.1, 50.8, 45.1, 44.4, 36.7, 36.2, 28.4, 28.2, 17.2, 16.9; IR (KBr, cm⁻¹): 1686, 1660; LRMS (EI, 70 eV) m/z (%): 381 (M⁺ + 1, 8), 380 (M⁺, 3), 176 (21), 105 (100); HRMS m/z (ESI) calcd for C₁₉H₂₁O₂ ([M + H]⁺) 281.1549, found 281.1536.

Methyl 2-methyl-5-oxo-4,5-diphenylpentanoate (3ah). d.r. = 3 : 2; 41.4 mg, 70%; Yellow oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.95 (t, J = 6.8 Hz, 2.0H), 7.47 (d, J = 6.8 Hz, 1.0H), 7.39 (d, J = 7.6 Hz, 2.0H), 6.31 (d, J = 10.0 Hz, 2.0H), 7.28 (s, 4.0H), 7.21 (s, 1.0H), 4.67 (s, 1.0H), 3.67 (s, 1.8H), 3.57 (s, 1.2H), 2.52–2.45 (m, 0.8H), 2.34 (m, 1.2H), 2.16–2.10 (m, 0.4H), 2.02–1.96 (m, 0.6H), 1.21 (d, J = 6.8 Hz, 1.2H), 1.15 (d, J = 6.8 Hz, 1.8H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.2 (2C), 176.8, 176.7, 143.5, 139.1, 138.7, 136.7, 136.4, 132.9, 129.0, 128.7, 128.6, 128.5, 128.4, 128.1 (2C), 127.2 (2C), 126.9, 51.6, 51.5, 51.3, 51.2, 37.9, 37.6, 37.4, 36.9, 18.0, 17.6; IR (KBr, cm⁻¹): 1728, 1686; LRMS (EI, 70 eV) m/z (%): 297 (M⁺ + 1, 16), 296 (M⁺, 8), 209 (8), 105 (100); HRMS m/z (ESI) calcd for C₁₉H₂₁O₃ ([M + H]⁺) 297.1497, found 297.1485.

N,2-Dimethyl-5-oxo-N,4,5-triphenylpentanamide (3ai). d.r. = 3 : 1; 54.2 mg, 73%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 8.03 (d, J = 7.6 Hz, 1.5H), 7.94 (d, J = 7.6 Hz, 0.5H), 7.49 (t, J = 6.8 Hz, 0.5H), 7.41 (t, J = 6.8 Hz, 1.5H), 7.31–7.24 (m, 4.5H), 7.20 (s, 3.5H), 7.17–7.11 (m, 1.0H), 6.74 (s, 2.0H), 4.82–4.78 (m, 0.8H), 4.63–4.59 (m, 0.3H), 3.25 (s, 2.2H), 3.18 (s, 0.8H), 2.50–2.43 (m, 1.0H), 2.36–2.28 (m, 1.0H), 2.02–1.95 (m, 1.0H), 1.07 (d, J = 6.8 Hz, 0.8H), 0.96 (d, J = 6.8 Hz, 2.3H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.9, 199.0, 176.2, 175.7, 143.4, 143.4, 139.4, 138.6, 136.7, 136.5, 136.4, 133.0, 132.8, 129.5, 129.3, 128.8 (2C), 128.7 (2C), 128.5 (2C), 127.9, 127.6, 127.5, 127.2, 127.0, 126.9 (2C), 50.9, 50.6, 38.5 (2C), 37.4, 36.8, 34.7, 34.2, 18.8, 18.5; IR (KBr, cm⁻¹): 1686, 1640; LRMS (EI, 70 eV) m/z (%): 372 (M⁺ + 1, 13), 371 (M⁺, 18), 256 (32), 105 (100); HRMS m/z (ESI) calcd for C₂₅H₂₆NO₂ ([M + H]⁺) 372.1946, found 372.1958.

2-Methyl-4,5-diphenyl-1-(piperidin-1-yl)pentane-1,5-dione (3aj). d.r. = 5 : 1; 50.3 mg, 72%; White solid; mp 115.1–116.3 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 8.00 (d, J = 7.2 Hz, 2.0H), 7.95 (d, J = 7.6 Hz, 0.4H), 7.46 (t, J = 6.8 Hz, 1.2H), 7.40–7.33 (m, 3.0H), 7.30–7.24 (m, 4.6H), 7.20 (t, J = 6.0 Hz, 1.2H), 4.73 (t, J = 4.8 Hz, 1.2H), 3.67 (t, J = 6.8 Hz, 1.0H), 3.53 (t, J = 6.8 Hz, 1.2H), 3.37 (t, J = 7.6 Hz, 0.2H), 3.22 (d, J = 4.8 Hz, 2.0H), 3.08 (d, J = 4.8 Hz, 0.4H), 2.78–2.73 (m, 0.2H), 2.52–2.46 (m, 2.0H), 2.30–2.14 (m, 0.5H), 1.98 (t, J = 8.8 Hz, 1.0H), 1.63–1.57 (m, 4.4H), 1.43 (s, 2.8H), 1.14 (d, J = 6.8 Hz, 0.6H), 1.08 (d, J = 6.0 Hz, 3.0H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.8, 173.8, 139.6, 138.9, 136.5, 133.0, 132.8, 128.8, 128.6, 128.5 (2C), 128.4, 128.1, 127.1, 50.9, 50.7, 46.2, 42.8, 38.7, 37.3, 33.1, 32.7, 26.3, 25.7, 25.5, 24.6, 24.4, 18.1; IR (KBr, cm⁻¹): 1686, 1651; LRMS (EI, 70 eV) m/z (%): 350 (M⁺ + 1, 19), 349 (M⁺, 23), 243 (16), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₂₈NO₂ ([M + H]⁺) 350.2128, found 350.2115.

Methyl 2-acetyl-2-ethyl-5-oxo-4,5-diphenylpentanoate (3ak). d.r. = 2 : 1; 35.2 mg, 52%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.90 (d, J = 8.4 Hz, 3.0H), 7.49–7.43 (m, 2.0H), 7.39–7.34 (m, 3.0H), 7.30–7.23 (m, 6.0H), 7.21–71.5 (m, 1.5H), 4.74–4.71 (m, 0.5H), 4.68–4.65 (m, 1.0H), 3.60 (s, 3.0H), 3.41 (s, 1.5H), 2.33–2.19 (m, 3.0H), 2.09 (d, J = 4.8 Hz, 4.5H), 2.06–1.95 (m, 2.0H), 1.90–1.81 (m, 1.0H), 0.80–0.76 (m, 4.6H); ¹³C NMR (100 MHz, CDCl₃) δ: 206.0, 205.2, 198.9, 198.7, 172.8, 172.7, 140.0, 139.7, 136.6, 136.4, 132.9, 132.8, 129.1, 129.0, 128.7 (2C), 128.5 (2C), 128.3, 128.2, 127.2, 127.1, 63.3, 63.2, 52.2, 52.1, 49.3, 48.9, 35.1, 34.8, 26.9, 26.8, 26.4, 25.9, 8.4, 8.3; IR (KBr, cm⁻¹): 1721, 1686, 1668; LRMS (EI, 70 eV) m/z (%): 353 (M⁺ + 1, 19), 352 (M⁺, 14), 248 (18), 105 (100); HRMS m/z (ESI) calcd for C₁₄H₁₈NO₃ ([M + H]⁺) 353.1747, found 353.1742.

Diethyl 2-methyl-2-(3-oxo-2,3-diphenylpropyl)malonate (3al). 61.1 mg, 80%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.94 (d, J = 7.2 Hz, 2H), 7.46 (t, J = 7.2 Hz, 1H), 7.37 (t, J = 7.2 Hz, 2H), 7.32–7.24 (m, 4H), 7.19–71.5 (m, 1H), 4.94–4.91 (m, 1H), 4.17–4.11 (m, 2H), 4.10–4.03 (m, 1H), 3.80–3.72 (m, 1H), 3.06–3.00 (m, 1H), 2.31–2.27 (m, 1H), 1.41 (s, 3H), 1.21 (t, J = 7.2 Hz, 3H), 1.03 (t, J = 7.2 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 198.5, 172.3, 171.6, 139.9, 136.3, 132.8, 129.0, 128.7, 128.5, 128.1, 127.0, 61.3, 61.2, 53.3, 49.6, 39.3, 21.6, 13.9413.6; IR (KBr, cm⁻¹): 1726, 1686; LRMS (EI, 70 eV) m/z (%): 383 (M⁺ + 1, 29), 382 (M⁺, 17), 277 (21), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₂₇O₅ ([M + H]⁺) 383.1853, found 383.1865.

Ethyl 2,2-difluoro-5-oxo-4,5-diphenylpentanoate (3am). 58.4 mg, 88%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.95 (d, J = 7.6 Hz, 2H), 7.48 (t, J = 7.6 Hz, 1H), 7.38 (t, J = 7.6 Hz, 2H), 7.29–7.25 (m, 4H), 7.22–7.18 (m, 1H), 4.97–4.94 (m, 1H), 4.20–4.12 (m, 1H), 4.09–4.01 (m, 1H), 3.35–3.21 (m, 1H), 2.61–2.47 (m, 1H), 1.21 (t, J = 7.2 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 197.3, 163.7 (t, J = 32.4 Hz), 137.8, 135.8, 133.2, 129.2, 128.8, 128.6, 128.2, 127.6, 115.3 (t, J = 249.1 Hz), 62.9, 46.8 (t, J = 3.85 Hz), 38.1 (J = 23.3 Hz, 1C), 13.7; ¹⁹F NMR (375 MHz, CDCl₃) δ: −104.3 (m), −104.4 (m); IR (KBr, cm⁻¹): 1770, 1686; LRMS (EI, 70 eV) m/z (%): 333 (M⁺ + 1, 221), 332 (M⁺, 12), 132 (17), 105 (100); HRMS m/z (ESI) calcd for C₁₉H₁₉F₂O₂ ([M + H]⁺) 333.1297, found 333.1315.

5-Phenyl-1,2-di-p-tolylpentane-1,5-dione (3ba). 35.6 mg, 50%; White solid; mp 97.8–98.5 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.91–7.86 (m, 4H), 7.53 (d, J = 7.6 Hz, 1H), 7.42 (t, J = 7.6 Hz, 2H), 7.19–7.16 (m, 4H), 7.08 (d, J = 8.0 Hz, 2H), 4.70 (t, J = 7.2 Hz, 1H), 3.10–2.85 (m, 2H), 2.60–2.49 (m, 1H), 2.34 (s, 3H), 2.29–2.18 (m, 4H); ¹³C NMR (100 MHz, CDCl₃) δ: 200.0, 199.3, 143.6, 136.8, 136.8, 136.3, 134.1, 133.0, 129.7, 129.2, 128.9, 128.5, 128.1, 128.0, 51.9, 36.1, 28.3, 21.6, 21.0; IR (KBr, cm⁻¹): 1692, 1674; LRMS (EI, 70 eV) m/z (%): 357 (M⁺ + 1, 14), 356 (M⁺, 21), 252 (17), 105 (100); HRMS m/z (ESI) calcd for C₂₅H₂₅O₂ ([M + H]⁺) 357.1873, found 357.1849.

1,2-Bis(4-chlorophenyl)-5-phenylpentane-1,5-dione (3ca). 55.4 mg, 70%; White solid; mp 82.9–83.8 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.89 (d, J = 8.4 Hz, 4H), 7.54 (t, J = 7.2 Hz, 1H), 7.43 (t, J = 7.6 Hz, 2H), 7.36 (d, J = 8.8 Hz, 2H), 7.27–7.20 (m, 4H), 4.74 (t, J = 7.2 Hz, 1H), 3.03–2.90 (m, 2H), 2.60–2.53 (m, 1H), 2.28–2.19 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.7, 198.1, 139.6, 137.3, 136.6, 134.6, 133.3, 133.2, 130.1, 129.6, 129.3, 128.9, 128.6, 127.9, 51.5, 35.5, 28.0; IR (KBr, cm⁻¹): 1708, 1674; LRMS (EI, 70 eV) m/z (%): 398 (M⁺ + 2, 13), 396 (M⁺, 18), 207 (6), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₁₉Cl₂O₂ ([M + H]⁺) 397.0762, found 397.0751.

1,2-Bis(4-bromophenyl)-5-phenylpentane-1,5-dione (3da). 53.5 mg, 55%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.89 (d, J = 8.4 Hz, 4H), 7.55 (t, J = 7.6 Hz, 1H), 7.43 (t, J = 7.6 Hz, 2H), 7.36 (d, J = 8.4 Hz, 2H), 7.28–7.20 (m, 4H), 4.73 (t, J = 7.6 Hz, 1H), 2.98–2.94 (m, 2H), 2.60–2.52 (m, 1H), 2.28–2.19 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.7, 198.1, 139.6, 137.3, 136.6, 134.6, 133.3, 133.2, 130.1, 129.6, 129.3, 128.9, 128.6, 127.9, 51.5, 35.5, 28.0; IR (KBr, cm⁻¹): 1697, 1674; LRMS (EI, 70 eV) m/z (%): 488 (M⁺ + 2, 10), 486 (M⁺, 19), 303 (12), 207 (24), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₁₉Br₂O₂ ([M + H]⁺) 486.9731, found 486.9745.

2,5-Diphenyl-1-(p-tolyl)pentane-1,5-dione (3ea). d.r. = 2 : 1; 42.4 mg, 62%; White solid; mp 88.3–89.6 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.97 (d, J = 7.6 Hz, 1H), 7.91–7.87 (m, 3H), 7.57–7.50 (m, 1H), 7.48–7.34 (m, 4H), 7.32–7.25 (m, 2H), 7.21–7.16 (m, 2H), 7.08 (d, J = 8.0 Hz, 1H), 4.77–4.71 (m, 1H), 3.05–2.88 (m, 2H), 2.60–2.54 (m, 1H), 2.33 (s, 2H), 2.31–2.22 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 200.0, 199.9, 199.7, 199.2, 143.7, 139.4, 136.8, 136.8, 136.6, 136.0, 134.1, 133.0, 132.8, 129.7, 129.2, 129.0, 128.9, 128.8, 128.7, 128.6, 128.5 (2C), 128.4, 128.3, 128.1, 128.0, 127.1, 126.8, 52.3, 52.0, 36.0, 36.0, 28.3, 28.2, 21.5, 21.0; IR (KBr, cm⁻¹): 1690, 1674; LRMS (EI, 70 eV) m/z (%): 343 (M⁺ + 1, 16), 342 (M⁺, 12), 223 (9), 119 (100); HRMS m/z (ESI) calcd for C₂₄H₂₃O₂ ([M + H]⁺) 343.1689, found 343.1691.

1-(4-Methoxyphenyl)-2,5-diphenylpentane-1,5-dione (3fa). 58.7 mg, 82%; White solid; mp 84.7–85.5 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.97 (d, J = 9.2 Hz, 2H), 7.90 (d, J = 7.6 Hz, 2H), 7.53 (t, J = 7.2 Hz, 1H), 7.42 (t, J = 7.6 Hz, 2H), 7.32–7.26 (m, 4H), 7.22–7.18 (m, 1H), 6.85 (d, J = 8.8 Hz, 2H), 4.72 (t, J = 7.2 Hz, 1H), 3.80 (s, 3H), 3.05–2.88 (m, 2H), 2.62–2.53 (m, 1H), 2.31–2.22 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 200.0, 198.1, 163.3, 139.6, 136.8, 133.0, 131.1, 129.6, 129.0, 128.5, 128.2, 128.0, 127.1, 113.7, 55.4, 52.0, 36.1, 28.3; IR (KBr, cm⁻¹): 1692, 1674; LRMS (EI, 70 eV) m/z (%): 359 (M⁺ + 1, 21), 358 (M⁺, 16), 135 (100); HRMS m/z (ESI) calcd for C₂₄H₂₃O₃ ([M + H]⁺) 359.1642, found 359.1651.

2-(4-Chlorophenyl)-1,5-diphenylpentane-1,5-dione (3ga). 50.7 mg, 70%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.96 (d, J = 7.2 Hz, 2H), 7.89 (d, J = 7.2 Hz, 2H), 7.56–7.48 (m, 2H), 7.45–7.37 (m, 4H), 7.25 (s, 4H), 4.79 (t, J = 7.2 Hz, 1H), 3.04–2.89 (m, 2H), 2.62–2.53 (m, 1H), 2.29–2.20 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.7, 199.3, 137.6, 136.7, 136.4, 133.1, 129.7, 129.2, 129.1, 128.8, 128.7, 128.6 (2C), 128.0, 51.5, 35.7, 28.1; IR (KBr, cm⁻¹): 1691, 1674; LRMS (EI, 70 eV) m/z (%): 364 (M⁺ + 2, 8), 362 (M⁺, 21), 224 (8), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₂₀ClO₂ ([M + H]⁺) 363.1152, found 363.1167.

1,5-Diphenyl-2-(4-(trifluoromethyl)phenyl)pentane-1,5-dione (3ha). 55.4 mg, 70%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.98 (d, J = 7.6 Hz, 2H), 7.89 (d, J = 7.2 Hz, 2H), 7.56–7.49 (m, 4H), 7.46–7.38 (m, 6H), 4.90 (t, J = 7.2 Hz, 1H), 3.06–2.92 (m, 2H), 2.67–2.58 (m, 1H), 2.33–2.24 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.6, 199.0, 143.2, 136.7, 136.3, 133.3, 133.2, 129.5 (q, J = 32.3 Hz), 128.7 (2C), 128.6, 128.0, 125.9 (q, J = 3.7 Hz), 125.3, 122.6, 51.9, 35.7, 28.2; ¹⁹F NMR (375 MHz, CDCl₃) δ: −62.5; IR (KBr, cm⁻¹): 1688, 1674; LRMS (EI, 70 eV) m/z (%): 397 (M⁺ + 1, 13), 396 (M⁺, 10), 224 (11), 105 (100); HRMS m/z (ESI) calcd for C₂₄H₂₀F₃O₄ ([M + H]⁺) 397.1415, found 397.1436.

1,5-Diphenyl-2-(m-tolyl)pentane-1,5-dione (3ia). The ¹H NMR spectrum of the crude product showed a 1 : 1 mixture of 3ia and a compound tentatively assigned as 3ia′ based on the methyl peak at δ 2.34 for 3ia and at δ 2.28 for 3ia′. 35.6 mg, 52%; White solid; mp 92.7–94.1 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.98 (d, J = 7.2 Hz, 1.0H), 7.90 (d, J = 7.6 Hz, 2.0H), 7.77 (t, J = 6.4 Hz, 1.0H), 7.53 (t, J = 7.2 Hz, 1.0H), 7.48–7.35 (m, 3.5H), 7.32–7.25 (m, 3.0H), 7.23–7.17 (m, 1.0H), 7.11 (s, 1.0H), 7.01 (d, J = 7.2 Hz, 0.5H), 4.79–4.71 (m, 1.0H), 3.05–2.87 (m, 2.0H), 2.63–2.53 (m, 1.0H), 2.31–2.22 (m, 2.5H); ¹³C NMR (100 MHz, CDCl₃) δ: 200.0, 199.9, 199.8, 199.6, 139.2, 139.0, 138.7, 138.3, 136.8, 136.6, 133.7, 133.0, 132.9, 129.2, 129.0, 128.8 (2C), 128.5 (2C), 128.3 (2C), 128.0, 127.2, 126.0, 125.5, 52.4 (2C), 36.0, 28.3, 21.4, 21.3; IR (KBr, cm⁻¹): 1688, 1674; LRMS (EI, 70 eV) m/z (%): 343 (M⁺ + 1, 33), 342 (M⁺, 15), 223 (13), 119 (100); HRMS m/z (ESI) calcd for C₂₄H₂₃O₂ ([M + H]⁺) 343.1689, found 343.1693.

(1,5-Diphenyl-2-(3-(trifluoromethyl)phenyl)pentane-1,5-dione (3ja). 51.5 mg, 65%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.98 (d, J = 7.2 Hz, 2H), 7.89 (d, J = 7.2 Hz, 2H), 7.60 (s, 1H), 7.56–7.48 (m, 4H), 7.45–7.40 (m, 5H), 4.90 (t, J = 7.2 Hz, 1H), 3.06–2.90 (m, 2H), 2.67–2.58 (m, 1H), 2.33–2.24 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.6, 199.1, 140.1, 136.7, 136.3, 133.3, 133.2, 131.7, 131.5, 131.2, 129.5, 128.7, 128.6, 128.0, 125.1 (q, J = 3.8 Hz), 124.2 (q, J = 3.7 Hz), 122.5, 51.8, 35.8, 28.4; ¹⁹F NMR (375 MHz, CDCl₃) δ: −62.5; IR (KBr, cm⁻¹): 1693, 1674; LRMS (EI, 70 eV) m/z (%): 397 (M⁺ + 1, 18), 396 (M⁺, 11), 224 (12), 105 (100); HRMS m/z (ESI) calcd for C₂₄H₂₀F₃O₄ ([M + H]⁺) 397.1415, found 397.1428.

1-(3,4-Dimethylphenyl)-2,5-diphenylpentane-1,5-dione (3ka). The ¹H NMR spectrum of the crude product showed a 2 : 1 mixture of 3ka and a compound tentatively assigned as 3ka′ based on the methyl peak at δ 2.16 for 3ka and at δ 2.10 for 3ka′. 32.8 mg, 46%; White solid; mp 98.4–99.3 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 8.06 (d, J = 7.2 Hz, 0.5H), 7.89 (d, J = 7.2 Hz, 1.0H), 7.81 (d, J = 7.6 Hz, 2.0H), 7.68 (s, 1.0H), 7.63 (d, J = 7.6 Hz, 1.0H), 7.55–7.51 (m, 1.0H), 7.44 (t, J = 7.2 Hz, 2.0H), 7.35–7.29 (m, 5.0H), 7.24–7.16 (m, 4.0H), 7.12–7.07 (m, 2.0H), 7.03 (d, J = 7.6 Hz, 1.0H), 6.96 (d, J = 7.2 Hz, 1.0H), 4.67 (t, J = 7.2 Hz, 1.0H), 4.61 (t, J = 7.2 Hz, 0.5H), 2.98–2.89 (m, 2.0H), 2.86–2.79 (m, 2.0H), 2.54–2.45 (m, 2.0H), 2.16 (d, J = 2.0 Hz, 6.0H), 2.10 (d, J = 3.6 Hz, 3.0H); ¹³C NMR (100 MHz, CDCl₃) δ: 200.0 (2C), 199.7, 199.4, 142.5, 139.5, 136.8 (2C), 136.4, 134.5, 133.0, 132.8, 130.2, 129.9 (2C), 129.7, 129.3, 128.9 (2C), 128.8, 128.5 (2C), 128.4, 128.2, 128.0, 127.8, 127.1, 126.8, 126.5, 125.8, 52.2, 52.0, 48.2, 36.1, 34.3, 29.7, 28.3, 19.9, 19.7, 19.3; IR (KBr, cm⁻¹): 1696, 1674; LRMS (EI, 70 eV) m/z (%): 357 (M⁺ + 1, 19), 356 (M⁺, 10), 223 (3), 133 (100); HRMS m/z (ESI) calcd for C₂₅H₂₅O₂ ([M + H]⁺) 357.1873, found 357.1861.

2-(3,4-Dichlorophenyl)-1,5-diphenylpentane-1,5-dione (3la). 64.9 mg, 82%; White solid; mp 84.1–85.3 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.96 (d, J = 7.2 Hz, 2H), 7.89 (d, J = 7.2 Hz, 2H), 7.56–7.50 (m, 2H), 7.45–7.39 (m, 5H), 7.35 (d, J = 8.0 Hz, 1H), 7.18–7.15 (m, 1H), 4.80 (t, J = 7.6 Hz, 1H), 3.05–2.90 (m, 2H), 2.62–2.54 (m, 1H), 2.28–2.20 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.5, 198.8, 139.3, 136.6, 136.1, 133.4, 133.2, 133.0, 131.4, 130.9, 130.2, 128.7, 128.7, 128.6, 127.9, 127.7, 51.1, 35.6, 28.1; IR (KBr, cm⁻¹): 1694, 1674; LRMS (EI, 70 eV) m/z (%): 398 (M⁺ + 2, 10), 396 (M⁺, 15), 264 (8), 173 (100); HRMS m/z (ESI) calcd for C₂₃H₁₉Cl₂O₂ ([M + H]⁺) 397.0762, found 397.0769.

2,5-Diphenyl-1-(o-tolyl)pentane-1,5-dione (3ma). 51.3 mg, 75%; White solid; mp 90.6–91.8 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.89 (d, J = 7.2 Hz, 2H), 7.58–7.51 (m, 2H), 7.42 (t, J = 7.6 Hz, 2H), 7.28–7.22 (m, 5H), 7.21–7.12 (m, 3H), 4.61 (t, J = 7.6 Hz, 1H), 3.05–2.89 (m, 2H), 2.66–2.57 (m, 1H), 2.33–2.25 (m, 4H); ¹³C NMR (100 MHz, CDCl₃) δ: 203.7, 199.8, 138.5, 138.2, 137.9, 136.8, 133.0, 131.6, 130.9, 128.9, 128.5, 128.4, 128.0, 127.2, 125.4, 55.4, 35.9, 27.5, 20.7; IR (KBr, cm⁻¹): 1710, 1674; LRMS (EI, 70 eV) m/z (%): 343 (M⁺ + 1, 13), 342 (M⁺, 8), 223(7), 119 (100); HRMS m/z (ESI) calcd for C₂₄H₂₃O₂ ([M + H]⁺) 343.1689, found 343.1695.

1-(2-Chlorophenyl)-2,5-diphenylpentane-1,5-dione (3na). 59.4 mg, 82%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.90 (d, J = 7.6 Hz, 2H), 7.53 (t, J = 7.6 Hz, 1H), 7.42 (t, J = 8.0 Hz, 2H), 7.32–7.20 (m, 7H), 7.15–7.08 (m, 2H), 4.59 (t, J = 7.6 Hz, 1H), 3.09–2.95 (m, 2H), 2.70–2.61 (m, 1H), 2.36–2.27 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 203.0, 199.7, 139.4, 137.3, 136.7, 133.0, 131.1, 130.4, 130.1, 128.9 (2C), 128.7, 128.5, 128.0, 127.5, 126.5, 56.8, 35.9, 26.9; IR (KBr, cm⁻¹): 1704, 1674; LRMS (EI, 70 eV) m/z (%): 364 (M⁺ + 2, 5), 362 (M⁺, 14), 223 (53), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₂₀ClO₂ ([M + H]⁺) 363.1152, found 363.1171.

2,5-Diphenyl-1-(2-(trifluoromethyl)phenyl)pentane-1,5-dione (3oa). 43.6 mg, 55%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.81 (d, J = 7.6 Hz, 2H), 7.58 (d, J = 7.6 Hz, 1H), 7.46 (t, J = 7.6 Hz, 1H), 7.40–7.30 (m, 4H), 7.23–7.12 (m, 5H), 6.99 (d, J = 7.6 Hz, 1H), 4.33 (t, J = 7.6 Hz, 1H), 2.98–2.81 (m, 2H), 2.61–2.52 (m, 1H), 2.30–2.21 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 203.4, 199.7, 139.6 (q, J = 1.8 Hz), 137.1, 136.8, 133.0, 131.4, 129.9, 129.0, 128.8, 128.5, 128.2, 127.9, 127.7, 126.6 (q, J = 5.0 Hz), 125.0, 122.3, 57.5, 35.6, 26.8; ¹⁹F NMR (375 MHz, CDCl₃) δ: −57.7; IR (KBr, cm⁻¹): 1688, 1674; LRMS (EI, 70 eV) m/z (%): 397 (M⁺ + 1, 21), 396 (M⁺, 14), 223 (49), 105 (100); HRMS m/z (ESI) calcd for C₂₄H₂₀F₃O₄ ([M + H]⁺) 397.1415, found 397.1432.

1-(2,5-Difluorophenyl)-2,5-diphenylpentane-1,5-dione (3pa). The ¹H NMR spectrum of the crude product showed a 3 : 2 mixture of 3pa and a compound tentatively assigned as 3pa′ based on the methine peak at δ 5.13 for 3pa and at δ 4.63 for 3pa′. 58.2 mg, 80%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.99 (d, J = 7.6 Hz, 1.2H), 7.92–7.88 (m, 2.0H), 7.56–7.50 (m, 1.6H), 7.44–7.42 (m, 3.6H), 7.30–7.20 (m, 2.0H), 7.12–7.07 (m, 0.4H), 7.04–6.96 (m, 1.6H), 6.90–6.84 (m, 1.6H), 5.13 (t, J = 7.2 Hz, 0.6H), 4.63 (t, J = 7.6 Hz, 0.4H), 3.10–2.88 (m, 2.0H), 2.64–2.56 (m, 1.0H), 2.29–2.19 (m, 1.0H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.6, 199.2, 198.5 (2C), 137.6, 136.7 (2C), 135.9, 133.4, 133.1, 133.0, 128.9, 128.7, 128.6 (2C), 128.5, 128.0 (2C), 127.5, 121.0, 120.9, 120.8, 120.7, 118.2, 118.1, 117.9 (2C), 117.1, 117.0, 116.9, 116.8, 116.7, 116.6, 115.7 (2C), 115.6 (2C), 115.4 (4C), 56.5, 56.4, 43.7, 36.0, 35.7, 27.7, 27.2.; ¹⁹F NMR (375 MHz, CDCl₃) δ: −115.3 (d, J = 18.4 Hz, 1F), −117.3 (d, J = 17.6 Hz, 1F), −117.6 (d, J = 18.8 Hz, 1F), −124.1 (d, J = 28.9 Hz, 1F); IR (KBr, cm⁻¹): 1710, 1674; LRMS (EI, 70 eV) m/z (%): 365 (M⁺ + 1, 16), 364 (M⁺, 9), 224 (11), 105 (100); HRMS m/z (ESI) calcd for C₂₃H₁₉F₂O₂ ([M + H]⁺) 365.1353, found 365.1369.

1-(2-Chlorophenyl)-2-(4-chlorophenyl)-5-phenylpentane-1,5-dione (3qa). 57.0 mg, 72%; White solid; mp 85.5–86.4 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 7.90 (d, J = 7.2 Hz, 2H), 7.55 (t, J = 7.6 Hz, 1H), 7.44 (t, J = 7.6 Hz, 2H), 7.34–7.28 (m, 2H), 7.27–7.23 (m, 2H), 7.20–7.11 (m, 4H), 4.61 (t, J = 7.6 Hz, 1H), 3.07–2.95 (m, 2H), 2.68–2.59 (m, 1H), 2.32–2.23 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 202.6, 199.5, 139.2, 136.7, 135.9, 133.4, 133.1, 131.4, 130.4, 130.3, 130.0, 129.1, 128.9, 128.6, 127.9, 126.7, 56.0, 35.7, 26.9; IR (KBr, cm⁻¹): 1782, 1674; LRMS (EI, 70 eV) m/z (%): 398 (M⁺ + 2, 7), 396 (M⁺, 10), 257 (30), 139 (100); HRMS m/z (ESI) calcd for C₂₃H₁₉Cl₂O₂ ([M + H]⁺) 397.0762, found 397.0777.

2-(Naphthalen-1-yl)-1,5-diphenylpentane-1,5-dione (3ra). 43.8 mg, 58%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 8.01 (d, J = 8.0 Hz, 2H), 7.88 (d, J = 7.2 Hz, 2H), 7.80–7.74 (m, 4H), 7.53–7.33 (m, 9H), 4.95 (t, J = 7.2 Hz, 1H), 3.08–2.92 (m, 2H), 2.72–2.63 (m, 1H), 2.43–2.34 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.9, 199.6, 136.7, 136.6 (2C), 133.6, 133.0, 132.9, 132.5, 128.9, 128.8, 128.5 (2C), 128.0, 127.7, 127.6, 127.2, 126.2, 125.9, 52.5, 35.9, 28.2; IR (KBr, cm⁻¹): 1710, 1674; LRMS (EI, 70 eV) m/z (%): 379 (M⁺ + 1, 22), 378 (M⁺, 12), 258 (11), 105 (100); HRMS m/z (ESI) calcd for C₂₇H₂₃O₃ ([M + H]⁺) 379.1711, found 379.1693.

1,5-Diphenyl-2-(thiophen-2-yl)pentane-1,5-dione (3sa). 56.8 mg, 85%; Red solid; mp 75.4–76.2 °C (uncorrected); ¹H NMR (400 MHz, CDCl₃) δ: 8.06 (d, J = 7.2 Hz, 2H), 7.90 (d, J = 7.2 Hz, 2H), 7.56–7.51 (m, 2H), 7.45–7.41 (m, 4H), 7.19–7.18 (m, 1H), 6.90–6.89 (m, 2H), 5.15 (t, J = 7.6 Hz, 1H), 3.09–2.94 (m, 2H), 2.65–2.56 (m, 1H), 2.36–2.28 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.7, 198.7, 141.1, 136.7, 136.0, 133.2, 133.1, 128.8, 128.6, 128.5, 128.0, 126.9, 126.0, 125.2, 46.7, 35.5, 29.0; IR (KBr, cm⁻¹): 1678, 1674; LRMS (EI, 70 eV) m/z (%): 335 (M⁺ + 1, 32), 334 (M⁺, 12), 229 (32), 105 (100); HRMS m/z (ESI) calcd for C₂₁H₁₉O₂S ([M + H]⁺) 335.1113, found 335.1100.

1,4-Diphenylhexane-1,5-dione (3ta). 39.9 mg, 75%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.89–7.87 (m, 2H), 7.56–7.52 (m, 1H), 7.45–7.41 (m, 2H), 7.36–7.32 (m, 2H), 7.30–7.28 (m, 1H), 7.21 (d, J = 6.8 Hz, 2H), 3.81 (t, J = 7.6 Hz, 1H), 2.96–2.81 (m, 2H), 2.50–2.41 (m, 1H), 2.16–2.11 (m, 1H), 2.07 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 208.1, 199.8, 138.4, 136.7, 133.1, 129.1, 128.6, 128.3, 128.0, 127.5, 58.4, 35.8, 29.1, 26.3; IR (KBr, cm⁻¹): 1674, 1652; LRMS (EI, 70 eV) m/z (%): 267 (M⁺ + 1, 17), 266 (M⁺, 8), 206 (11), 105 (100); HRMS m/z (ESI) calcd for C₁₈H₁₉O₂ ([M + H]⁺) 267.1385, found 267.1393.

Methyl 5-(2-chlorophenyl)-2-methyl-5-oxo-4-phenylpentanoate (3nh). d.r. = 1 : 1; 49.5 mg, 75%; Yellow oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.32 (d, J = 7.6 Hz, 1.0H), 7.28–7.21 (m, 4.0H), 7.19–7.10 (m, 3.0H), 7.10–7.06 (m, 1.0H), 4.52–4.48 (m, 1.0H), 3.67 (s, 1.5H), 3.60 (s, 1.5H), 2.57–2.46 (m, 1.0H), 2.38–2.20 (m, 1.6H), 2.07–2.00 (m, 0.6H), 1.22 (d, J = 7.2 Hz, 1.5H), 1.17 (d, J = 6.8 Hz, 1.5H); ¹³C NMR (100 MHz, CDCl₃) δ: 202.6 (2C), 176.7, 176.5, 139.4, 139.3, 137.0, 136.9, 131.2, 131.1, 130.4 (2C), 130.2, 130.1, 128.9, 128.8 (2C), 128.6, 127.5 (2C), 126.5 (2C), 55.7, 55.6, 51.6, 51.5, 37.4, 36.8, 36.0, 35.9, 18.0, 17.4; IR (KBr, cm⁻¹): 1711, 1704; LRMS (EI, 70 eV) m/z (%): 332 (M⁺ + 2, 6), 332 (M⁺, 16), 236 (10), 139 (100); HRMS m/z (ESI) calcd for C₁₉H₂₀ClO₃ ([M + H]⁺) 331.1101, found 331.1109.

Diethyl 2-(3-(2-chlorophenyl)-3-oxo-2-phenylpropyl)-2-methylmalonate (3nl). 70.7 mg, 85%; Colorless oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.30–7.25 (m, 3H), 7.22 (t, J = 6.4 Hz, 2H), 7.17 (t, J = 6.0 Hz, 4H), 4.66 (t, J = 6.0 Hz, 1H), 4.14–4.09 (m, 2H), 4.06–3.98 (m, 1H), 3.87–3.79 (m, 1H), 3.05–2.99 (m, 1H), 2.45–2.40 (m, 1H), 1.43 (s, 3H), 1.22 (t, J = 7.2 Hz, 3H), 1.14 (t, J = 7.2 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 200.8, 172.2, 171.7, 138.7, 137.6, 131.3, 130.9, 130.3, 129.1, 128.9, 128.7, 127.4, 126.4, 61.3, 61.2, 53.7, 53.0, 37.1, 21.1, 13.9, 13.8; IR (KBr, cm⁻¹): 1726, 1704; LRMS (EI, 70 eV) m/z (%): 418 (M⁺ + 2, 5), 416 (M⁺, 13), 177 (14), 139 (100); HRMS m/z (ESI) calcd for C₂₃H₂₆ClO₅([M + H]⁺) 417.1469, found 417.1684.

Ethyl 5-(2-chlorophenyl)-2,2-difluoro-5-oxo-4-phenylpentanoate (3nm). 60.0 mg, 82%; Yellow oil; ¹H NMR (400 MHz, CDCl₃) δ: 7.32–7.27 (m, 2H), 7.25–7.21 (m, 4H), 7.19–7.15 (m, 3H), 4.80 (t, J = 6.4 Hz, 1H), 4.16–4.07 (m, 2H), 3.33–3.19 (m, 1H), 2.69–2.55 (m, 1H), 1.25 (t, J = 7.2 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 199.7, 163.7 (t, J = 32.4 Hz), 138.2, 135.8, 131.6, 130.9, 130.4, 129.1, 129.0, 128.7, 127.9, 126.5, 115.3 (t, J = 249.2 Hz), 62.9, 51.0 (t, J = 3.8 Hz), 36.6 (t, J = 23.5 Hz), 13.7; ¹⁹F NMR (375 MHz, CDCl₃) δ: −103.4 (d, J = 258.8 Hz), −104.0 (d, J = 258.8 Hz); IR (KBr, cm⁻¹): 1770, 1704; LRMS (EI, 70 eV) m/z (%): 368 (M⁺ + 2, 7), 366 (M⁺, 21), 165 (15), 139 (100); HRMS m/z (ESI) calcd for C₁₉H₁₈ClF₂O₃ ([M + H]⁺) 367.0913, found 367.0927.

Acknowledgements

We thank the Natural Science Foundation of China (no. 21172060), Specialized Research Fund for the Doctoral Program of Higher Education (no. 20120161110041), and Hunan Provincial Natural Science Foundation of China (no. 13JJ2018) for financial support.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: Copies of ¹H and ¹³C spectra. CCDC 1407703. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5qo00220f

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